The present invention relates generally to a scroll compressor and more particularly to such a compressor having a flywheel to prevent reverse scroll rotation.
Optimal efficiency and low noise operation of a scroll compressor is highly dependent on the contact forces between the mating scrolls, with the obvious design compromise being to provide enough force to ensure good sealing while generating minimal frictional force components.
Axial and radial sealing are the most critical techniques and have been recognized by U.S. Pat. No. 801,182 which recommended forcing the orbiting scroll axially to the fixed scroll by means of a mechanical spring.
Tip-to-base loading associated with axial compliance can be maintained also by gas loading of the orbiting scroll. Gas pressure is applied underneath of the orbiting scroll to load it against the fixed scroll. Biasing pressure may be provided by discharge gas supplied to the cavity located underneath of the orbiting scroll from the discharge plenum of the scroll compressor or by forming on the back of the orbiting scroll a so-called back pressure chamber with intermediate gas pressure tapped from the compression pockets through vents in the orbiting scroll baseplate. Very often a combination of gas and spring axial loading systems are used in scroll compressors.
The radial compliance techniques described in U.S. Pat. No. 1,906,142 and U.K. Patent No. 486,192 employ the centrifugal force of the rotating parts to produce the radial component from the pressure load by a mechanism such as the swing link. Radial compliance is related to the ability of the orbiting scroll to seek its own orbit path as defined by the wrap geometry in order to maintain outward flank contact. Flank contact is ensured if the centrifugal force of the orbiting scroll mass is sufficient to overcome the radial internal gas forces. A scroll compressor designed for operation at a constant speed cannot be operated at variable speed when only a moderate contact pressure between the orbiting scroll member and stationary scroll member is obtained for a specific rotation speed.
The centrifugal force acting on an orbiting scroll member is reduced from the design level when the rotation speed has come down below the design rotational speed. This undesirable situation permits the orbiting scroll wrap to oscillate on the stationary scroll wrap forming a large radial gap between both scroll wraps, so as to allow the gas under compression to leak to the low pressure side. A following change of the intermediate and discharge gas pressure will effect the axial gas load on the back of the orbiting scroll. This fluctuating, decreasing pressure will trigger upward-downward movement of the orbiting scroll causing impacts of the orbiting scroll tips against the base of the stationary scroll and consequently extensive noise.
Almost the same phenomena can occur after a split-second power interruption or at shut-down of a normal run cycle. The consequence of a split-second interruption is backward rotation of the compressor motor rotor, crankshaft, and attached orbiting scroll. When the power is restored after a split-second interruption, the compressor may continue to run in reverse for several minutes with noticeable noise, until the internal motor protector trips.
At shut-down of a normal run cycle, the compressor will run backward for several seconds with extensive sound and vibration until internal pressures equalize. As disclosed in U.S. Pat. No. 4,998,864, some scroll compressors incorporate a clutch coupled to the drive shaft which permits rotation in only one direction. The clutch rollers are designed with a wedge angle that enable them to engage into the clutching component when reverse rotation occurs. Performing as a roller bearing when orbiting scroll rotates in the normal "forward" direction, the clutch contributes to energy losses, wear of the crankshaft, and additional vibration.